This invention relates to apparatus and methods for the handling of radioactive material, and especially to the loading, removal, and replacement of filters used in nuclear power generating stations to remove radioactive impurities in the primary and secondary water systems.
More particularly, the invention relates to an apparatus capable of control from a remote station and of performing all of the procedures required for changing a filter and for loading the spent radioactive filter in a shielded container for disposal.
In a nuclear power plant, a coolant is circulated around the core of the reactor as a heat transfer medium that transfers the heat generated in the reactor to apparatus wherein the heat may be further transferred and/or extracted. Coolant branch circuits are provided, and they are utilized for many purposes, such as coolant volume control, coolant water chemistry control, reactivity control, etc. The reactive coolant system, its associated branch circuits (commonly known as auxiliary process systems) and their related components comprise a major portion of the fluid system of a nuclear power plant or other nuclear reactor installation.
During operation of a nuclear reactor or other source of radioactivity, particles of foreign matter resulting from corrosion of the coolant and auxiliary process piping become entrained in the coolant and circulate therewith around the core of the reactor and through the associated cooling and process equipment and piping. As the particles flow around the source of radioactivity, they become radioactive and tend to accumulate at various locations in the piping systems and emit radioactive energy. Depending upon the shielding associated with the piping system, the radiation from the accumulated particles tends to create health hazards for personnel working in and about the radioactive fluid systems and/or associated components.
In order to control the quantity of foreign matter flowing in the cooling and process systems, nuclear power plants and other installations are provided with filters to collect the radioactive particles for removal from the coolant and process systems. Some conventional filter housings employed to capture radioactive particles have a top hatch permitting installation and removal of a filter cartridge from above. The particle-laden cartridge is usually placed in a shielded shipping container for ultimate disposal.
The most common filtering equipment in use today employs disposable filter cartridges that entrap the radioactive solids during the course of the filtering action. Such filter cartridges must be replaced periodically.
The filter cartridge is usually located in a filter pit below the floor of the power plant, and covered with a shield plug forming part of the floor. Since the filter cartridges become highly radioactive during use, they are located within shielded rooms having walls with a thickness of several feet on all sides. Removal of the spent cartridge begins with removal of the shield plug, using an overhead hoist or the like, laying the shield plug aside, and exposing the filter assembly beneath the floor. The operator must remain behind a shield wall to prevent overexposure to the radiation yielded by the assembly. Once the filter pit is opened, a shielded drum or transfer cask is positioned adjacent the pit and a cartridge-grappling tool or the like is lowered in place to grasp the filter cartridge. The cartridge is then withdrawn and placed in the drum or transfer cask. Upon verification that the cartridge is in the transfer cask, the cask is removed from its position adjacent the access opening and transferred to a disposal area.
It can be appreciated that the removal and reloading of filters is very hazardous and great care must be taken to protect the operator. The method and apparatus of the present invention resolve many of the difficulties mentioned above and afford other features and advantages heretofore not obtainable.